In a photoresist process as one of semiconductor fabrication processes, a resist is coated on the surface of a semiconductor wafer (hereinafter, referred to as a wafer), and then, the resist is exposed with a predetermined pattern and developed so as to form a resist pattern. Such a treatment is generally performed by using a system including a coating/developing apparatus connected to an exposure device, the coating/developing apparatus being configured to perform the coating and development process for the resist.
In the coating/developing apparatus, a heat treatment module is provided which is for heating a wafer before/after coating or development of a resist. The heat treatment module has a heat plate (e.g., a hot plate) on which one wafer is individually disposed and heated. The heat plate includes a seating plate, and a heater such as a heating resistor for heating the seating plate.
In order to improve a throughput, a plurality of heat treatment modules is provided for performing a predetermined process in a photoresist process in the coating/developing apparatus. Then, wafers are simultaneously undergone the heat treatment process in each of the heat treatment modules. A temperature adjuster for supplying power to the heat plate and adjusting the temperature has parameters fixed as, for example, general use conditions. Accordingly, even if a plurality of heat treatment modules is provided for performing a predetermined process as described above, the same parameters may be used among the respective heat treatment modules.
However, the resistance value of the heater may be varied due to the environmental changes during the fabrication of the heat plate. As a result, a rated power (e.g., Wattage) may be varied. In a heat treatment module, a heat plate having, for example, a heater output power ranging from 1300 W to 1800 W at an input voltage to of 200V as a specification may be embedded. Also, in a case of an AC power source for supplying power to the heater, an input voltage applied to the heater may be varied. For example, when the input voltage is set as 200V as a specification, an actual input voltage may be varied within a range of 170V to 242V. Due to the variation of the rated wattage of the heater, and the variation of the input voltage of the heater, as described above, wafers which are subjected to heating processes may have a different thermal history therebetween, and also critical dimensions of resist patterns formed in the wafers may be varied.
Also, an electric device for supplying power to each heat plate, which includes a cable, a breaker, or the like, has to be configured in such a manner that the electric device can withstand the load at a maximum voltage and a heater's maximum rated wattage within the range of operation-assured voltage of the AC power source. Specifically, for example, as described above, when the rated wattage ranges from 1300 W to 1800 W, and an input voltage specification ranges from 170V to 242V, the load is assumed based on a heat plate's maximum rated wattage of 1800 W, and a maximum input voltage of 242V. Herein, since the current is calculated as 242V÷((200V)2÷1800 W)=10.9 A, an electric device capable of flowing such a high current has to be selected. For this reason, the electric device becomes larger, thereby increasing fabrication cost.
Japanese Laid-Open Patent Publication No. 2007-53191 discloses a technology for controlling a thermal history of a substrate by controlling the power of a heat plate of a heat treatment module. However, in the technology, a method for controlling a current value to withstand the variation of AC voltage, and the variation of a heater's resistance value is not described. Thus, it is not possible to solve the above described problems.